Electromagnetic alarm device



I J. H. RUBENSTEIN 2,355,395

ELECTROMAGNETIC ALARM DEVICE Filed Nov. 6, 1942 4 Sheets-Sheet l HIGH GAIN AMP.

& RELAY MILPA.

HTTURNEYS.

Aug. 8, 94 J. H. RUBENSTEIN 2,355,395

ELECTROMAGNETIC ALARM DEVICE v Filed Nov. 6, 1942 4 Sheets-Sheet 2 m saw/v HMP.

& RELAY mgz,

MIlF/q HTTORNEYS.

Aug; 4- J. H. RUBENSTEIN 2,355,395-

' ELECTROMAQNETIC ALARM DEVICE Filed Nov. 6, 1942" 4 Sheets-Sheet 5 f/770/FNEY5.

8, 4- J. H. RUBENSTEIN ELECTROMAGNETIC ALARM DEVICE Filed Nov. 6, 1942 4 Sheets-Sheet 4 --tem is extremely expensive of the general type i or conductors extending into or around the area it is permissible to Patented {\ug. 8, 1944 UNITED STATES PATENT OFFl 2,855,895 ELECTROMAGNETIC ALARM DEVICE Jacob H. Rubensteh, Syracuse, N. Y. Application November I, 1942, Serial No. 484,820

2 (mm. (CL 117-352) This invention relates to alarm devices of thetype employed to signal the approach of persons or objects in proximity to a guarded area, particularly large areas such as the property of manufacturing plants, ammunition dumps. Oil storage areas, harbors, and the like.

Various electrically operated alarm systems are now employed for this purpose. For example, the area to be protected may be encircled by a series of microphones, the system being arranged so that the microphones pick up any vibration made by a person or object approaching the particular microphone, and the microphone is cooperable with other apparatus in the system to give an alarm at a central to install and, of course, is operable to give an alarm only when the approaching person or object causes'sound waves'or'vibrations to be impressed upon the microphone. This prohibits use of such a system station. This sysantenna of loop if noisy operations are necessarily carried on in proximity'of the perimeter of the guarded area.

Another system employs a wire'or fence serving in the capacity of an antenna for radio apparatus which is operable upon change in capacity between the antenna and the ground to cause an alarm to be given. The chief disadvantage of this system resides in the fact that the antenna can not; be more than 400 or 500 feet in length. Otherwise, the established capacity between the antenna and the ground is so great, relative to any change effected by a person or obiect approaching the antenna, that such change sumcient to actuate the alarm ap-.

will not be paratus.

My invention has as an object an alarm system referred to, including a pair to beprotected, the conductors being connected to electrical apparatus which is operable when a person or object approaches within proximity of theconductors along any-point thereof, and the invention embodies a novel arrangement whereby extend the conductors a disof feet, all whereby areas sevcan be economically and ellitance ,of thousands erai acres in extent ciently protected.

, The invention consists in the novel features l and in the combinations and constructions hereinafter set forth and claimed.

In describing this invention,;reference is made to the accompanying drawings in which like characters designate corresponding partsin all the views.

ot the relay or alarm Figure 1 is a schematic ,wiring diagram illus'- trating a circuit in which my invention is carried out.

Figure 2 is a view. similar to Figure 1, illusttgating a modified arrangement of the conducrs. Figure 8 is a diagrammatic view illustrating a further modification of the circuit employing form.

Figure 4 is a schematic diagram of the circuit embodying a further modificationin part.

The invention consists generally of a pair of The invention further includes energizing one oi the conductors, the antenna radiator, with a source of alternating current, the frequency of which is preferably in the higher audio range, or the lower radio range, the frequency depending upon the length of the conductors. alternating current must be a pure sine wave substantially free from harmonics. The conductors are so arranged relatively that the second positioned in the electro-magnetic induction field of the energized conductor and accordingly is thereby. This second conductor is connected to second tuned resonant circuit is connected to a source of alter hating current having the same wave characteristics and the same amplitude as the current in said second conductor. These two tuned resonant circuits are coupled to what may be termed a bridge circuit, the arrangement being such as to produce substantially zero current in the center connection or leg of is connected to a relay or suitable indicating device. With this arrangement, a person or object approaching in the magnetic "field anywhere along the extent of the conductors effects a dis- .tortion of such field effecting inturn a change in the amplitude or phase ,of the current in the second conductor, and this change results in increasing the value of the current in the center leg of the bridge circuit. and thereby causing operation device connected thereto.

In Figure l. the conductors II, I i extend around one-half of the perimeter of the guarded area A,

and a second pair of conductors II. II extend around the other half of the perimeter of the also energized the bridge which, in turn,

guarded area. The conductors it, l2 are energized by a master oscillator power amplifier ll of conventional construction. The amplifier is coupled to an antenna. coupling circuit through the line I. The antenna coupling circuit includes a coil i1 and a variable condenser IS. The conductor II is connected to th coil i1 through variable condenser II and adjustable tap 20. The conductor I2 is likewise connected to the coil i1 through a variable condenser 2i and a tap 22. It will be understood that the antenna coupling circuit and condensers ll, 2| are employed to impress the proper wave length on the conductors II and i2, this, of course, varying with the actual length of these conductors.

The conductors l0 and i2 may be termed antenna radiators, and the conductors I I It may be referred to as pick-up antennas or receivers. The conductors II, II, and II, It extend in parallel spaced apart relationship. In practice, they are that under normal conditions there is zero current flowing in the center leg 36 and accordingly zero current to the high gain amplifier. Under these conditions, i! a person or object approaches the conductors ll, H, or l2, it, the eiectro-magnetic field is distorted causing a change in either phase or amplitude oi' the current in the pick-up conductors II, II. This results in an unbalanced condition in the bridle circuit as will be obvious, permitting current to be fed from either coil 21 or 2| through the center leg II to the high gain amplifier causlog the alarm device to operate.

.In Figure 2, the system employs a single pair of conductors ll, ii. The conductor ii is connected to the tuned resonant circuit including the coil 2! and variable condenser 26, this cirmounted upon posts, or other suitable supports, preferably with the, pick-up conductors II, It,

about three feet from the ground, and the con- The conductors are, of course, insulated from each other and from ground. The oscillator amplifier II functions to impress a pure sine wave,

practically free from harmonics, upon the an-.

ductors l0, I! about six feet from the ground.

tent'proportional to the amount of power prcduced by the oscillator amplifier it.

Each of the pick-up conductors ii, ii are connected to a tuned resonant circuit. This circuit, to which the conductor II is connected, includes a coil 22 and variable condenser 24, and the resonant circuit, to which conductor I3 is connected, includes coil 2!, variable condenser 28. Each of these tuned resonant circuits is, in turn, couto one side of a bridge circuit. For example, the coil 22 is coupled to coil 21 through link cult being coupled to coil 2O 01' the bridge circult throush link line 3|. The coil 21 ot the bridge circuit is similarly coupled to a tuned resonant circuit including coil 23, condenser 24, through link line". This latter tuned resonant circuit may be fed directly from one oi the grids of the final stage of the amplifier througha blocking condenser and line, as 54, which will be well understood, the arrangement in all other respects being similar to that shown in Figure 1. This circuit is advantageous in certain conditions where it is not practical to extend the two pairs of antenna and pick-up conductors, However, wherethedevice is employed to guard an outside area, the circuit shown in Figure 1 has some advantages over that shown in Figure 2 due to the fact that any external or atmospheric.

matically balancing.

line 28, and coil 25 is similarly coupled to coil 2! through link line .30. The opposite sides of the bridge circuitinclude variable resistance 3i. Like ends of coils 21, 28 and coils 25, 23 are connected to a grounded conductor 84. The func- 7 tion of the tuned resonant circuits is to match the phase of the current in coils 21, 29 of the bridge circuit. This can be done with great accuracy inasmuch as the energizing current in the antenna radiators ll, i2 is of pure sine wave quality to start with. Preferably, the tuned I880:

nant circuits are shielded, as indicated in dotted outlines'in Figure 3.

The conductor 38 constitutes the center leg of the bridge being connected at one and between the coils 21, 29, and being provided with a variable tap 31 at the opposite end, coacting with resistance ii. The function of the variable tap I? is to permit an adjustment of the bridge circuit so, that the current flowing in the central leg I! is of zero value.

The central leg 36 is connected to a suitable relay or alarm'device. This connection may be direct, or through means to amplifythe current depending, of course, on the amount of energy picked up by conductors ii, H3 in a particular installation. 'As here shown, the central leg 38 is connected to coil 40 of a step-up transformer Ii. The secondary coil 42 being connected to a conventional high gain amplifier 42 through lines 44, 45.

A previously stated, the tap 31 is adjusted so In Figure 3, I illustrate the invention in a modified circuit which is advantageous over both the circuits shown in Figures 1 and 2 in certain circumstances. In this circuit, the master oscillator power amplifier ii is employed to energize an antenna loop 60, the amplifier being coupled to the loop through the conventional antenna tuning circuit including coil Cl and variable condenser 62. In this case, the pick-up conductor is in the nature of a receiving loop 83, this loop being connected to the tuned resonance circuit including coil 2!, condenser 2l and condenser M. The tuned resonant circuit, including the coil 23, condenser 24, is fed directly from the amplifier ll through line It, as illustrated in Figure 2. This loop arrangement is adapted for use in circumstances where it may not be practical to install antenna conductors. as shown in Figures 1 and 2. In some installations it may be advantageous to use a combination of antennas as, for example, if the system is employed on a vessel the radiating antenna may be oi the conductor type i9 trailing from the vessel, and the receiving antenna may consist of a loop i3.

Figure 4 illustrates a modification of the tuned resonant circuits to which the pick-up conductors M, It are connected. This modified structure is advantageously employed if the conductors ldi I; i2--i3 are of relatively long lengths wherein the greater capacity between the pick-up comntduitliltolg;t and the ground, might lead to difllc y 0 aining the pro r ha bridgeaircuit. pe p Se balancemthe The conductors I I, ii are connected respectiveassaaos ployed to impress a negative bias on the grids ll, 14, as will be well understood. function of the tubes 15, II is to isolate the conductors II, it from the respective tuned resonant circuits.

What I claim is:

1. An electromagnetic alarm device comprising a pair of conductors extending in proximity to the area to be protected and being insulated from each other and from ground, one oi said conductors being energized with a source of a1- ternating current, the other of said conductors being positioned in the magnetic induction field of said first conductor and being energized thereby, said second conductor being connected to a tuned resonant circuit, a second tuned resonant circuitconnected to an alternating current source having the same wave characteristics as the current in said second conductor, one of said tuned resonant circuits including means operable to vary the phase of the current therein to match the phase of the current in said other tuned res onant circuit, said tuned resonant circuits being coupled respectively to opposite sides of a bridge circuit, an eleetro-responsive device connected to the center leg of said bridge circuit, and means operable to normally eiiect substantially zero current in said center leg.

2. An electromagnetic alarm device comprising a first pair of radiating and pick-up antennas positioned in proximity to a portion of the area to be protected, a second pair of radiating and pick-up antennas positioned in proximity to another portion oi the area to be protected, each' of said radiating antennas being energized with a source of alternating current and each pick-up antenna being positioned in the magnetic induction field ofeach radiating antenna respectively and being energized thereby, each of said pickup antennas being connected to a tuned resonant circuit, one of said resonant circuits including means operable to adjust ther phase of said circuit to match the phase of the current in said other tuned resonant circuit, and said tuned resonant circuits being coupled respectively to the opposite sides of a bridge circuit, the center leg oi said bridge circuit including means adjustable to produce a current of predetermined value in said'center leg, an electro-responsive alarm means connected to said center leg and being operable upon change of the value of the current therein upon distortion of the magnetic induction held of either radiating antenna.

JACOB E RUBENBTEIN. 

